Their points allowed per game has remained in the 21-23 range since Week 3, and overall their third-down prevention rate has been near the bottom of the standings.

The Patriots are still allowing long passes, including two against the Dolphins a week ago that turned third-and-longs into a fresh set of downs. They now have had 59 passes of 20 or more yards completed against them, and still lead the league.

But to watch the defense over the past few weeks, it looks like an improved unit, and the hope is that continues in Monday night’s game against the Houston Texans at Gillette Stadium.

It isn’t just the turnovers being forced, because those have been there all season. The defense has at least one in every game, and New England’s 33 takeaways were second in the league, one behind Chicago heading into Week 14’s slate of games.

Thanks to the offense being stingier than Scrooge when it comes to giving the ball away, the Patriots’ ratio is tops in the league. Coach Bill Belichick has said many a time that you won’t win many games in the NFL if you lose the turnover battle.

What seems to be happening is that this young defensive unit, with 19 of 26 players age 26 or younger, is starting to hit its stride. It is learning the nuances of the playbook and learning how to play with confidence and with one another.

That is leading to key plays at key moments.

The Dolphins did get two third-down conversions with completions of 22 and 20 yards, but Miami only had three on 13 chances in the loss. Some of those missed opportunities for Miami were questionable decisions by a rookie quarterback, but some, as on third and 4 from the Miami 26, were because of the defense’s play: Trevor Scott beat Nate Garner and strip-sacked Ryan Tannehill; Vince Wilfork recovered.

The turnover became a short field goal and 17-3 New England lead.

On Thanksgiving night at MetLife Stadium, Jerod Mayo stopped Shonn Greene for a 1-yard gain on third and 2 in the first quarter, and in the second quarter Mayo sacked Mark Sanchez for a 9-yard loss on third and 6.

The offensively inept Jets might not be the best measuring stick for a defense, but the Patriots did stop New York on seven of their 10 third-down situations.

The defense jump-started the team against Indianapolis. New England was trailing, 14-7, early in the second quarter, with rookie quarterback Andrew Luck having moved his team down the field fairly easily on the Colts’ first two possessions.

Wilfork batted down a third-down pass attempt, forcing a punt; Julian Edelman returned the punt for the tying touchdown.

Less than a minute later, Aqib Talib turned an easy interception into an impressive return, putting the Patriots ahead. They never trailed again and went on to blow out the Colts.

Over the first six games of the season, when the Patriots went 3-3, it was close to 50-50 that a team could get a first down against this defense.

During their current six-game win streak, that third-down conversion number has gone from 48.4 percent to 43.8, and it has gone down further in recent weeks: the Bills converted 7 of 11 chances in Week 10, the high mark of the season, but the Colts were 8 for 14 and the Jets and Dolphins were a combined 6 for 23 (26 percent).

After that listless first quarter against Indianapolis, Belichick was seen kneeling in front of all of the defensive players on the bench, furiously drawing on a whiteboard. It probably isn’t a coincidence that the unit played much better the rest of the game.

In the weeks since, Belichick frequently has turned his back to the field while the offense was working, secure in the knowledge that Tom Brady and offensive coordinator Josh McDaniels can steer that group through any situation.

It was also against the Colts that Talib played his first game with New England after serving the final game of his league-mandated suspension the week before. Talib has shown lapses in concentration and discipline, but even when he’s floundering he’s still the best full-time cornerback on the roster.

The presence of Talib means Kyle Arrington has been able to move inside, where he is stronger as the nickel cornerback.

The secondary also has gained its own “quarterback” with Devin McCourty moved back to safety permanently. McCourty can use his on-field smarts when he’s back deep and able to see the entire offense in front of him instead of being on one quarter of the field lined up on one player.

McCourty communicates what he sees to his teammates, which has settled things on the back end of the defense, which had been the weak area of the unit for two years.

Offensively, the Patriots didn’t have their best game in Miami. But Wilfork confidently announced afterward that it was all right if Brady & Co. weren’t at their best once in a while — the defense has the offense’s back.

That hasn’t often been the case in recent seasons. If that remains true as December turns to January and the playoffs begin, the Patriots will be a far more complete team than they were last year.

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